Palladium-Catalyzed Tandem Approach to 3-(Diarylmethylene)oxindoles Using Microwave Irradiation

Article abstract of DOI:10.1055/s-0035-1560091

We developed a rapid and efficient microwave-assisted tandem reaction for the synthesis of 3-(diarylmethylene)oxindoles. Three palladium-catalyzed reactions (Sonogashira, Heck, and Suzuki-Miyaura reactions) were combined under microwave irradiation conditions to produce 3-(diarylmethylene)oxindoles from simple propiolamides, aryl iodides, and arylboronic acids. The addition of Ag₃PO₄ enhanced the yield and stereoselectivity of the tandem reaction significantly.

Full text of DOI:10.1055/s-0035-1560091

SYNLETT
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© Georg Thieme Verlag Stuttgart · New York
2015, 26, 2296–2300
letter
2296
S. Park et al.
Letter
Synlett
Palladium-Catalyzed Tandem Approach to 3-(Diarylmethylene)-
oxindoles Using Microwave Irradiation
Sunhwa Park
R1
R2
R1
Kye Jung Shin
Jae Hong Seo*
Pd(PPh3)4, CuI
NaOAc, DMF
PPh3, Ag3PO4
R2
B(OH)2
Br
I
+
Integrated Research Institute of Pharmaceutical Sciences,
College of Pharmacy, The Catholic University of Korea,
Bucheon-si, Gyeonggi-do 420-743, Republic of Korea
jaehongseo@catholic.ac.kr
MW
150 °C, 10 min
O
N
R
Me
R
N
O
70–99% yield
16 examples
high E/Z ratio
Me
Received: 14.06.2015
Accepted after revision: 10.07.2015
Published online: 12.08.2015
two-operation, one-pot reactions into a three-component
tandem reaction and outline the substrate scope of the re-
action.
DOI: 10.1055/s-0035-1560091; Art ID: st-2015-u0441-l
Ar1
Abstract We developed a rapid and efficient microwave-assisted tan-
dem reaction for the synthesis of 3-(diarylmethylene)oxindoles. Three
palladium-catalyzed reactions (Sonogashira, Heck, and Suzuki–Miyaura
reactions) were combined under microwave irradiation conditions to
produce 3-(diarylmethylene)oxindoles from simple propiolamides, aryl
iodides, and arylboronic acids. The addition of Ag3PO4 enhanced the
yield and stereoselectivity of the tandem reaction significantly.
Br
Heck/
Suzuki–Miyaura
Sonogashira
Br
Ar2B(OH)2
90 °C
Ar1I
60 °C
N
R
O
N
R
2
O
1
Key words microwave irradiation, Sonogashira reaction, Heck reac-
tion, Suzuki–Miyaura reaction, tandem reaction
Ar1I
Ar2B(OH)2
Ar2
Ar1
previous work
one-pot
two operations
this work
one-pot
one operation
O
Multicomponent tandem reactions have attracted inter-
est from organic chemists because they can allow the syn-
thesis of complex molecules from simple compounds in a
time-saving and economically favorable manner.1 The ap-
proach also constitutes a powerful tool for diversity-orient-
ed synthesis (DOS), which provides an efficient method for
the preparation of small-molecule chemical libraries in me-
dicinal chemistry.2 As part of our ongoing effort to develop
novel multicomponent tandem reactions for biologically
active heterocycles, we recently reported an efficient, one-
pot synthetic method for 3-(diarylmethylene)oxindoles,3
which possess intriguing biological activities such as antidi-
abetic4 and anticancer properties.5 This method combined
a Sonogashira reaction of the electron-deficient propiol-
amide 1 and a Heck/Suzuki–Miyaura domino reaction of
the resulting Sonogashira adduct 2 (Scheme 1). To achieve
high yield and efficiency of the one-pot reaction, two sepa-
rate operations are required. Thus, after completion of the
Sonogashira reaction at 60 °C, the addition of arylboronic
acid and elevation of the reaction temperature to 90 °C are
required to facilitate the Heck/Suzuki–Miyaura domino re-
action. Here, we report on the conversion of the previous
N
multicomponent tandem
R
3
Scheme 1 Synthesis of 3-(diarylmethylene)oxindoles by combining
three palladium-catalyzed reactions
First, three substrates (propiolamide 4, phenyliodide,
and 4-chlorophenylboronic acid) were added to the reac-
tion mixture at the beginning of the reaction and the result-
ing mixture was exposed to the previous one-pot reaction
conditions with sequential temperature and time control
(60 °C, 1.5 h followed by 90 °C, 24 h). Under these condi-
tions, the desired 3-(diarylmethylene)oxindole
6 was
formed in good yield (78%) with a small amount of biphenyl
7 formed as by-product (12% yield), which was produced by
a direct Suzuki–Miyaura reaction between phenyl iodide
and 4-chlorophenylboronic acid (Table 1, entry 1). However,
the E/Z stereoselectivity of olefin was moderate (E/Z ratio =
2:1). In our previous work, the same problem of low E/Z ste-
reoselectivity was overcome through the addition of a silver
salt at the second step; this may suppress E/Z isomerization
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Letter
Synlett
Table 1 Optimization of the Tandem Reaction Conditionsa
Cl
PhI, 4-ClPhB(OH)2
Pd(PPh3)4, CuI
NaOAc, DMF
Ph
Br
Cl
Br
ligand, additive
+
+
N
O
temp, time
thermal or MW
N
O
O
Me
Me
N
4
Me
5
6
7
Entry
Thermal or MW
Ligand (mol%)
Additive (equiv)
Temp, time
Yield (%)b
Ratio (E/Z)d
5
6c
7
1
2
thermal
thermal
thermal
thermal
thermal
MW
–
–
60 °C, 1.5 h, then 90 °C, 24 h
60 °C, 1.5 h, then 90 °C, 24 h
60 °C, 1.5 h, then 90 °C, 24 h
90 °C, 24 h
–
78
39
50
67
61
80
92
99
98
92
36
12
13
23
31
36
–
2:1
–
Ag3PO4 (1.1)
Ag3PO4 (1.1)
Ag3PO4 (1.1)
Ag3PO4 (1.1)
Ag3PO4 (1.1)
Ag3PO4 (1.1)
Ag3PO4 (1.1)
Ag3PO4 (1.1)
Ag3PO4 (1.1)
–
8
4:1
3
PPh3 (30)
PPh3 (30)
PPh3 (30)
PPh3 (30)
PPh3 (30)
PPh3 (30)
PPh3 (30)
–
–
5:1
4
–
7.5:1
3.5:1
8:1
5
150 °C, 3 h
–
6
100 °C, 1 h
10
–
7
MW
130 °C, 10 min
–
13:1
13:1
7.5:1
8:1
8
MW
150 °C, 10 min
–
–
9
MW
160 °C, 5 min
–
–
10
11
MW
150 °C, 10 min
–
–
MW
PPh3 (30)
150 °C, 10 min
34
–
1:1.2
a Reaction conditions: 4 (0.1 mmol), PhI (1.1 equiv), 4-ClPhB(OH)2 (1.2 equiv), Pd(PPh3)4 (10 mol%), CuI (5 mol%), NaOAc (3.0 equiv), ligand, additive, DMF,
thermal or microwave conditions.
b Isolated yield.
c Combined yield of isolated E- and Z-products.
d Ratio between isolated E- and Z-products.
of the vinyl palladium intermediate of the Heck reaction by
converting the catalytic cycle from the neutral pathway into
the cationic pathway.3 Thus, we performed the same reac-
tion with the addition of Ag3PO4,6 which increased the E/Z
ratio to 4:1, as expected, but substantially decreased the
product yield to 39% with the remaining Sonogashira ad-
duct 5 (8% yield) (entry 2).
To enhance the efficiency of the reaction by securing
the stability of the Pd catalyst, we tested reactions with var-
ious phosphine ligands and found that the addition of PPh3
increased the yield to 50% (Table 1, entry 3). Interestingly,
when the reaction was started at 90 °C, improved yield and
stereoselectivity was observed (67%, E/Z = 7.5:1, entry 4).
However, high starting temperature promoted the genera-
tion of biphenyl by-product 7 (31% yield). Increasing the re-
action temperature to 150 °C allowed for a shorter reaction
time (3 vs. 24 h), and the reaction afforded 6 in similar yield
but with lower stereoselectivity (61% yield, E/Z = 3.5:1, en-
try 5). The last two results (entries 4 and 5) revealed that
high reaction temperature could facilitate the tandem reac-
tion, even in the presence of Ag3PO4. Thus, we exposed the
reaction mixture to microwave irradiation conditions,
which allowed the reaction mixture to reach a high energy
state in a short time.7 We found that microwave irradiation
at 100 °C for 1 h provided the desired oxindole 6 with good
yield and stereoselectivity (80% yield, E/Z = 8:1), despite the
remaining intermediate 5 (10% yield) (entry 6). Irradiation
at 130 °C significantly decreased the reaction time to 10
min to provide 6 with higher yield and stereoselectivity
(92% yield, E/Z = 13:1; entry 7). The best results were ob-
tained under microwave irradiation at 150 °C for 10 min,
which afforded 6 in an excellent yield with high stereoselec-
tivity (99% yield, E/Z = 13:1; entry 8). Reaction at a higher
temperature of 160 °C completed the reaction in a shorter
time (5 min) with good product yield (98%), but slightly de-
creased stereoselectivity (E/Z = 7.5:1; entry 9). To investi-
gate the role of additives, control reactions were performed
without PPh3 or Ag3PO4. The reaction without PPh3 showed
slightly lower yield and stereoselectivity (92 vs. 99% yield,
E/Z = 8:1 vs. 13:1; entry 10 vs. 8). However, when the reac-
tion was performed without Ag3PO4, 6 was formed with
complete loss of stereoselectivity (E/Z = 1:1.2) in very low
yield (36%), and a substantial amount of the Sonogashira
adduct 5 remained (34% yield; entry 11). This result sug-
gested that Ag3PO4 is a key additive for enhancing the yield
and stereoselectivity of the microwave-assisted tandem re-
action.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 2296–2300

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By using the optimal microwave-assisted reaction con-
ditions, we investigated the substrate scope of the reaction.
Symmetrically substituted 3-(diarylmethylene)oxindoles
9a–d were synthesized from propiolamide 4 with the cor-
responding aryl iodides and arylboronic acids in good
yields, regardless of substituents on both aryl substrates
(72–90% yield; Table 2, entries 1–4). To explore the substit-
uent effect on propiolamide 4, 5-methoxyphenyl propiol-
amide 8a, and 5-chlorophenyl propiolamide 8b were used
for the synthesis of symmetrically substituted oxindoles,
which also produced the desired products 9e–h in high
yield (81–94% yield; entries 5–8). We then explored the
synthesis of unsymmetrically substituted 3-(diarylmethy-
lene)oxindoles, which was expected to be more challenging
considering the stereoselectivity of the reaction. When
phenyl iodide was used as one of the three substrates, the
tandem reaction proceeded smoothly to afford the corre-
sponding products 9i and 9j with high yield and stereose-
lectivity (85 and 89% yield, E/Z = 8:1 and 9.5:1; entries 9
and 10). Reaction with a relatively electron-rich 4-me-
thoxyphenyl iodide as substrate also gave the desired oxin-
dole 9i in good yield (80% yield), but resulted in a stereose-
lectivity issue (E/Z = 1.2:1; entry 11). After extensive ef-
forts, the E/Z ratio of the product could be improved to 1:4
by irradiation at 100 °C for 1 h (entry 12). Interestingly, re-
action with 3-methoxyphenyl iodide, bearing the same me-
thoxy substituent at a different position, proceeded with
good yield and stereoselectivity (85% yield, E/Z = 1:8, entry
13). Aryl iodides with electron-withdrawing substituents,
such as chloro and nitro groups, underwent the tandem re-
action to give 6 and 9j with good yield (85 and 88%, respec-
tively) and excellent stereoselectivity (E/Z = 1:15 and 1:26,
respectively) (entries 14 and 15). These results suggested
that the stereoselectivity of the reaction is affected signifi-
cantly by both the electron-different characteristics of sub-
stituents on the aryl iodide and by the substituent posi-
tions. A heterocyclic moiety, such as the 4-pyridinyl group,
could also be introduced by using this method to afford (E)-
9l as the sole detectable isomer in good yield (77%; entry
16).
Table 2 Substrate Scope of the Microwave-Assisted Tandem Reactiona
Ar1I, Ar2B(OH)2
Pd(PPh3)4, CuI
NaOAc, DMF
PPh3, Ag3PO4
Ar2
Ar1
O
Br
R
N
O
MW, 150 °C, 10 min
N
R
Me
Me
4 or 8
Ar1
Ph
6 or 9
Entry
4/8
R
Ar2
Ph
6/9
Yield (%)b
Ratio (E/Z)c
1
2
4
H
H
H
H
9a
9b
9c
9d
9e
9f
9g
9h
9i
75
75
72
90
90
92
81
94
85
89
80
70d
85
85
88
77
–
4
4-MeOC6H4
4-ClC6H4
4-O2NC6H4
4-MeOC6H4
4-O2NC6H4
4-MeOC6H4
4-O2NC6H4
Ph
4-MeOC6H4
–
3
4
4-ClC6H4
4-O2NC6H4
4-MeOC6H4
4-O2NC6H4
4-MeOC6H4
4-O2NC6H4
4-MeOC6H4
4-O2NC6H4
Ph
–
4
4
–
5
8a
8a
8b
8b
4
MeO
MeO
Cl
–
6
–
7
–
8
Cl
–
9
H
8:1
9.5:1
1.2:1
1:4
1:8
1:15
1:26
>25:1
10
11
12
13
14
15
16
4
H
Ph
9j
4
H
4-MeOC6H4
4-MeOC6H4
3-MeOC6H4
4-ClC6H4
4-O2NC6H4
Ph
9i
4
H
Ph
9i
4
H
Ph
9k
6
4
H
Ph
4
H
Ph
9j
4
H
4-pyridinyl
9l
a Reaction conditions: 4 or 8 (0.1 mmol), Ar1I (1.1 equiv), Ar2B(OH)2 (1.2 equiv), Pd(PPh3)4 (10 mol%), CuI (5 mol%), NaOAc (3.0 equiv), DMF, microwave irradia-
tion, 150 °C, 10 min.
b Combined yield of isolated E- and Z-products.
c Ratio between isolated E- and Z-products.
d The reaction was conducted at 100 °C for 1 h.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 2296–2300

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Ag3PO4 has been reported to be one of the most effective
silver salt additives for enhancing the rate of the Heck reac-
tion of aryl or alkenyl halides, which is likely due to the for-
mation of cationic Pd(II) complexes by abstracting halide
from the neutral Pd(II) complex of the oxidative addition
step.8 To determine the effect of Ag3PO4 on each step of our
tandem reaction, two separate reactions were tested
(Scheme 2). When desbromo propiolamide 10 was exposed
to the tandem reaction conditions without Ag3PO4, Sono-
gashira product 11 formed in 77% yield. On the other hand,
the addition of Ag3PO4 increased the yield of the reaction to
99%, which suggested that Ag3PO4 is a beneficial additive for
enhancing the rate of the Sonogashira reaction.9 The results
from the Heck/Suzuki–Miyaura reaction were more dra-
matic. Under standard conditions with Ag3PO4, Sonogashira
adduct 5 was successfully transformed into oxindole 6 with
excellent yield and stereoselectivity (93% yield, E/Z = 13:1).
However, the same reaction without Ag3PO4 resulted in an
incomplete reaction (5; 34% remained) with poor product
yield and low stereoselectivity (54% yield, E/Z = 5:1). Over-
all, these results suggested that Ag3PO4 plays an important
role in both steps of the tandem reaction. The enhanced
yields and stereoselectivities under microwave irradiation
conditions are probably due to faster reaction rate than that
achieved under thermal conditions. Thus, high energy state
of microwave irradiation reduced the suppressing effect of
Ag3PO4 on the Sonogashira reaction to decrease the chance
of direct Suzuki–Miyaura reaction of aryl iodides and aryl-
boronic acids. Fast Heck/Suzuki–Miyaura reaction made the
corresponding vinylpalldium intermediates exist for a rela-
tively short period, which reduced the chance of E/Z isom-
erization of the intermediates, resulting in high stereoselec-
tivity of the products.
simple to perform (10 min, microwave irradiation), uses
readily available substrates (propiolamides, aryl iodides,
and arylboronic acids), and displays high tolerance to sub-
stituents on the substrates. Further studies that are focused
on elaborating the details of the mechanism with the silver
salt and on extending the substrate scope of the reaction
are underway in our laboratory.
Acknowledgment
This research was supported by the Basic Science Research Program
through the National Research Foundation of Korea (NRF) funded by
the Ministry of Science, ICT
&
Future Planning (NRF-
2014R1A1A1038332), and Research Fund 2011 of The Catholic Uni-
versity of Korea.
Supporting Information
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0035-1560091.
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References and Notes
(1) For selective reviews of multicomponent tandem reaction, see:
(a) D’Souza, D. M.; Müller, T. J. J. Chem. Soc. Rev. 2007, 36, 1095.
(b) Shiri, M. Chem. Rev. 2012, 112, 3508. (c) Rotstein, B. H.;
Zaretsky, S.; Rai, V.; Yudin, A. K. Chem. Rev. 2014, 114, 8323.
(d) Kaïm, L. E.; Grimaud, L. Eur. J. Org. Chem. 2014, 7749.
(2) For selective reviews of diversity-oriented synthesis (DOS)
related to multicomponent reactions, see: (a) Rujiter, E.;
Scheffelaar, R.; Orru, R. V. A. Angew. Chem. Int. Ed. 2011, 50,
6234. (b) Dömling, A.; Wang, W.; Wang, K. Chem. Rev. 2012, 112,
3083. (c) Kotha, S.; Chavan, A. S.; Goyal, D. ACS Comb. Sci. 2015,
17, 253.
(3) Dong, G. R.; Park, S.; Lee, D.; Shin, K. J.; Seo, J. H. Synlett 2013, 24,
1993.
(4) Yu, L.-F.; Li, Y.-Y.; Su, M.-B.; Zhang, M.; Zhang, W.; Zhang, L.-N.;
Pang, T.; Zhang, R.-T.; Liu, B.; Li, J.-Y.; Li, J.; Nan, F.-J. ACS Med.
Chem. Lett. 2013, 4, 475.
PhI
Ph
Pd(PPh3)4, CuI
NaOAc, DMF, PPh3
MW, 150 °C, 10 min
N
O
(5) (a) Lv, K.; Wang, L.-L.; Zhou, X.-B.; Liu, M.-L.; Liu, H.-Y.; Zheng,
Z.-B.; Li, S. Med. Chem. Res. 2013, 22, 1723. (b) Pal, A.; Ganguly,
a.; Ghosh, A.; Yousuf, M.; Rathore, B.; Banerjee, R.; Adhikari, S.
ChemMedChem 2014, 9, 727.
(Ag3PO4)
N
O
Me
with Ag3PO4 93%
without Ag3PO4 77%
Me
10
11
(6) According to unpublished results from our group, Ag3PO4 is a
better silver salt additive for the reaction than AgOTf, which
was used in previous work (see ref. 3).
Cl
Ph
PhI
(7) For selective reviews of microwave-assisted reaction, see:
(a) Lidström, P.; Tierney, J.; Wathey, B.; Westman, J. Tetrahedron
2001, 57, 9225. (b) Kappe, C. O. Angew. Chem. Int. Ed. 2004, 43,
6250. (c) de la Hoz, A.; Díaz-Oritz, Á.; Moreno, A. Chem. Soc. Rev.
2005, 34, 164. (d) Herrero, M. A.; Kremsner, J. M.; Kappe, C. O. J.
Org. Chem. 2008, 73, 36. (e) Singh, B. K.; Kaval, S.; Tomar, S.;
Eycken, E. V.; Parmar, V. S. Org. Process Res. Dev. 2008, 12, 468.
(8) (a) Karabelas, K.; Westerlud, C.; Hallberg, A. J. Org. Chem. 1985,
50, 3896. (b) Cabri, W.; Candiani, I.; Bedeschi, A.; Penco, S. J. Org.
Chem. 1992, 57, 1481. (c) Ashimori, A.; Overman, L. E. J. Org.
Chem. 1992, 57, 4751. (d) Weibei, J.-M.; Blanc, A.; Pale, P. Chem.
Rev. 2008, 108, 3149.
Pd(PPh3)4, CuI
Br
NaOAc, DMF, PPh3
ΜW, 150 °C, 10 min
N
O
O
(Ag3PO4)
N
Me
with Ag3PO4 93% (E/Z = 13:1)
without Ag3PO4 54% (E/Z = 5:1)
Me
5
6
Scheme 2 Effects of silver salt on each step of the tandem reaction
In conclusion, we developed a novel microwave-assist-
ed, three-component tandem reaction for the synthesis of
3-(diaylmethylene)oxindoles.10 This method is rapid and
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 2296–2300

2300
S. Park et al.
Letter
Synlett
(9) For examples of silver-mediated Sonogashira reaction, see:
(a) Zou, G.; Zhu, J.; Tang, J. Tetrahedron Lett. 2003, 44, 8709.
(b) Yang, F.; Wu, Y. Eur. J. Org. Chem. 2007, 3476. (c) Zhou, M.-B.;
Wei, W.-T.; Xie, Y.-X.; Lei, Y.; Li, J.-H. J. Org. Chem. 2010, 75,
5635.
1700, 1604, 1096, 734 cm–1
.
1H NMR (500 MHz, CDCl3): δ =
7.43–7.41 (m, 3 H), 7.33–7.29 (m, 3 H), 7.15 (td, J = 7.7, 1.0 Hz,
1 H), 6.95 (d, J = 7.8 Hz, 1 H), 6.91 (dd, J = 8.3, 1.9 Hz, 1 H), 6.83
(t, J = 1.9 Hz, 1 H), 6.76 (d, J = 7.8 Hz, 1 H), 6.66 (td, J = 7.7,
1.0 Hz, 1 H), 6.42 (d, J = 7.6 Hz, 1 H), 3.76 (s, 3 H), 3.20 (s, 3 H).
13C NMR (125 MHz, CDCl3): δ = 166.8, 159.3, 154.3, 143.5, 141.5,
141.3, 129.3, 129.3, 129.1, 128.9, 128.9, 124.5, 123.3, 122.5,
121.5, 115.7, 114.4, 107.8, 55.4, 26.0. HRMS (EI): m/z calcd for
(10) Palladium-Catalyzed Tandem Reaction under Microwave
Irradiation; General Procedure: A microwave reaction vial was
charged with N-methylpropiolamide (0.5 mmol, 1.0 equiv), aryl
iodide (0.55 mmol, 1.1 equiv), aryl boronic acid (0.65 mmol,
1.3 equiv), CuI (0.025 mmol, 5 mol%), NaOAc (1.5 mmol, 3.0
equiv), Pd(PPh3)4 (0.05 mmol, 10 mol%), Ag3PO4 (0.55 mmol, 1.1
equiv), and DMF (5 mL). The reaction vial was sealed and
exposed to microwave irradiation conditions for the indicated
time and temperature. The mixture was cooled to 25 °C and
diluted with EtOAc (200 mL). The organic layer was washed
with H2O (3 × 30 mL) and brine (30 mL), then dried (Na2SO4), fil-
tered, and concentrated under reduced pressure. The crude
residue was purified by column chromatography (silica gel;
hexane–EtOAc) to give 3-(diarylmethylene)oxindoles 6 and 9.
(Z)-3-[(3-Methoxyphenyl)(phenyl)methylene]-1-methylin-
dolin-2-one [(Z)-9k]: Yellow solid; mp 118.2 °C; Rf = 0.21 (silica
gel; hexanes–EtOAc, 4:1). IR (film): 3535, 3055, 2927, 2214,
C
23H19NO2: 341.1416; found: 341.1422.
(E)-3-[(3-Methoxyphenyl)(phenyl)methylene]-1-methylin-
dolin-2-one [(E)-9k]: Yellow solid; mp 53.0 °C; Rf = 0.26 (silica
gel; hexanes–EtOAc, 4:1). IR (film): 3287, 3055, 2937, 1700,
1604, 1469, 1094, 698 cm–1 1H NMR (500 MHz, CDCl3): δ =
.
7.37–7.33 (m, 6 H), 7.16 (td, J = 7.7, 1.1 Hz, 1 H), 6.98 (ddd, J =
8.3, 2.6, 0.9 Hz, 1 H), 6.77 (dt, J = 9.9, 1.9 Hz, 1 H), 6.84 (dd, J =
2.5, 1.6 Hz, 1 H), 6.76 (d, J = 7.8 Hz, 1 H), 6.69 (td, J = 7.7, 1.0 Hz,
1 H), 6.48 (d, J = 7.3 Hz, 1 H), 3.77 (s, 3 H), 3.20 (s, 3 H). 13C NMR
(125 MHz, CDCl3): δ = 166.9, 160.1, 154.4, 143.5, 142.7, 139.9,
130.2, 130.0, 129.2, 128.9, 128.0, 124.4, 123.5, 123.3, 121.7,
121.6, 115.0, 114.5, 107.8, 55.5, 26.0. HRMS (EI): m/z [M+] calcd
for C23H19NO2: 341.1416; found 341.1417.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 2296–2300